The present invention relates to a light source unit using light emitting diodes, an illuminating apparatus, and a display apparatus using this illuminating apparatus for illuminating a non-light emitting image display panel.
An improved light emitting efficiency of recent light emitting diodes (LED) drives an ever replacement of light sources for a variety of illuminating apparatuses from fluorescent lamps to light emitting diodes. This is because the light emitting diodes have many features such as smaller size, ability to generate multiple colors, ease of control, low power consumption and the like. However, since light output of a single light emitting diode is still insufficient in applications which require high light outputs, a plurality of light emitting diodes are arrayed to make up an illuminating apparatus.
For example, in a liquid crystal display (liquid crystal display apparatus) which is a typical example of a display apparatus using a non-light emitting image display panel, an illuminating apparatus is made up of an array of plural light emitting diode packages, which emit light red, green, and blue light, respectively, for use as a back light, as described in SID03 Digest, pp. 1262-1265 (2003). Also, as described in SID04 Digest, pp. 1222-1225 (2004), a red, a green, and a blue light emitting diode are disposed in the same package, a plurality of which are arranged in combination with light guiding plates to build an illuminating apparatus which is used as a back light. Further, JP-A-8-339707, JP-U-7-1804, JP-A-7-235624, JP-A-2000-262265, JP-A-2001-351404, Japanese Patent No. 2519341, JP-U-2521493, and JP-A-9-33924 describe signal lamps for automobile, each of which has light emitting diodes mounted on a series of lead frames.
However, when light emitting diodes are packaged and a plurality of the resulting packages are arrayed as described in SID03 Digest, pp. 1262-1265 (2003) and SID04 Digest, pp. 1222-1225 (2004), each package must be again mounted on a printed circuit board by soldering or the like, thus causing an increased cost for the mounting, and a problem with regard to the reliability due to the double mounting, i.e., mounting of light emitting diodes in packages, and mounting of the packages on a printed circuit board.
On the other hand, when a plurality of light emitting diodes area arrayed on a series of lead frames as described in JP-A-8-339707, JP-U-7-1804, JP-A-7-235624, JP-A-2000-262265, JP-A-2001-351404, Japanese Patent No. 2519341, JP-U-2521493, and JP-A-9-33924, the mounting cost can be reduced because the light emitting diodes are connected to the lead frames at a smaller number of spots. However, when the signal light is used for illuminating a non-light emitting image display panel which needs a white illumination light source, the signal light is disadvantageous in the light utilization efficiency and thickness in order to mix red, green, and blue color light to generate white illuminating light, particularly when red, green, and blue light emitting diodes are used, because of the lack of color mixing means.